High temperature membranes based on PBI/sulfonated polyimide and doped-perovskite nanoparticles for PEM fuel cells

Rubbery Soft Polymer Electrolyte Membrane with a Nanomatrix Channel Prepared from Natural Rubber

Rubbery soft polymer electrolyte membranes (PEMs) prepared from naturally occurring products are in high demand for the fabrication of flexible fuel cells as a multipurpose energy source to achieve a carbon-neutral society. This work describes the preparation of a rubbery soft PEM from deproteinized natural rubber (DPNR) by grafting-copolymerizing ethyl p-styrenesulfonate (SSEt) onto the surface of rubber particles in the latex stage, followed by hydrolysis with NaOH and cast film formation to construct a nanomatrix channel. The resulting rubbery soft PEM, a graft copolymer of DPNR and poly(p-styrenesulfonic acid) (DPNR-graft-PSS), is characterized by 1H NMR spectroscopy, transmission electron microscopy (TEM), impedance analysis, and tensile testing. The hydrophobic rubber particles with a diameter of about 1 μm are well dispersed in the continuous nanochannel of hydrophilic poly(p-styrenesulfonic acid) with a thickness of about 10 nm that possesses a high proton conductivity, owing to an efficient proton transportation, which is beneficial for polymer electrolyte fuel cells. σ* is the proton conductivity per unit equivalent of sulfonic acid, which is distinguished from the proton conductivity, σ. The value of σ* for the DPNR-graft-PSS prepared with 1.0 mol/kg-rubber of SSEt is 2.6 (S/cm)/meq, which is approximately 1.4 times higher than that of the perfluorosulfonic acid membrane Nafion117, whereas its σ is lower. The apparent activation energy of DPNR-graft-PSS (3.2 kJ/mol) is lower than that of Nafion117, and its stress at break (6.9 MPa) is higher than that of DPNR. The high σ*, low apparent activation energy, and outstanding tensile strength of DPNR-graft-PSS can be attributed to the formation of the nanomatrix channel.

Confined Nano-Channels Incorporated with Multi-Quaternized Cations for Highly Phosphoric Acid Retention HT-PEMs

Developing a new strategy to retain phosphoric acid (PA) to improve the performance and durability of high-temperature proton exchange membrane fuel cell (HT-PEMFC) remains a challenge. Here, a strategy for ion-restricted catcher microstructure that incorporates PA-doped multi-quaternized poly(fluorene alkylene-co-biphenyl alkylene) (PFBA) bearing confined nanochannels is reported. Dynamic analysis reveals strong interaction between side chains and PA molecules, confirming that the microstructure can improve PA retention. The PFBA linked with triquaternary ammonium side chain (PFBA-tQA) shows the highest PA retention rate of 95%. Its H2/O2 fuel cell operates within 0.6% voltage decay at 160 °C/0% RH, and it also runs over 100 h at 100 °C/49% RH under external humidification. This combination of high PA retention, and chemical and dimensional stability fills a gap in the HT-PEMFC field, which requires strict moisture control at 90-120 °C to prevent acid leaching, simplifying the start-up procedure of HT-PEMFC without preheating.

Study of Innovative GO/PBI Composites as Possible Proton Conducting Membranes for Electrochemical Devices

The appeal of combining polybenzimidazole (PBI) and graphene oxide (GO) for the manufacturing of membranes is increasingly growing, due to their versatility. Nevertheless, GO has always been used only as a filler in the PBI matrix. In such context, this work proposes the design of a simple, safe, and reproducible procedure to prepare self-assembling GO/PBI composite membranes characterized by GO-to-PBI (X:Y) mass ratios of 1:3, 1:2, 1:1, 2:1, and 3:1. SEM and XRD suggested a homogenous reciprocal dispersion of GO and PBI, which established an alternated stacked structure by mutual π-π interactions among the benzimidazole rings of PBI and the aromatic domains of GO. TGA indicated a remarkable thermal stability of the composites. From mechanical tests, improved tensile strengths but worsened maximum strains were observed with respect to pure PBI. The preliminary evaluation of the suitability of the GO/PBI X:Y composites as proton exchange membranes was executed via IEC determination and EIS. GO/PBI 2:1 (IEC: 0.42 meq g^-1; proton conductivity at 100 °C: 0.0464 S cm^-1) and GO/PBI 3:1 (IEC: 0.80 meq g^-1; proton conductivity at 100 °C: 0.0451 S cm^-1) provided equivalent or superior performances with respect to similar PBI-based state-of-the-art materials.

Construction of Highly Conductive Cross-Linked Polybenzimidazole-Based Networks for High-Temperature Proton Exchange Membrane Fuel Cells

High-temperature proton exchange membrane fuel cells (HT-PEMFCs) are of great interest to researchers in industry and academia because of their wide range of applications. This review lists some creative cross-linked polybenzimidazole-based membranes that have been prepared in recent years. Based on the investigation into their chemical structure, the properties of cross-linked polybenzimidazole-based membranes and the prospect of their future applications are discussed. The focus is on the construction of cross-linked structure of various types of polybenzimidazole-based membranes and their effect on proton conductivity. This review expresses the outlook and good expectation of the future direction of cross-linked polybenzimidazole membranes.

Development of WO3-Nafion Based Membranes for Enabling Higher Water Retention at Low Humidity and Enhancing PEMFC Performance at Intermediate Temperature Operation

The proton exchange membrane (PEM) represents a pivotal material and a key challenge in developing fuel cell science and hydrogen technology. Nafion is the most promising polymer which will lead to its commercialisation. Hybrid membranes of nanosized tungsten oxide (WO₃) and Nafion were fabricated, characterised, and tested in a single cell. The incorporation of 10 wt% WO₃ resulted in 21% higher water uptake, 11.7% lower swelling ratio, almost doubling the hydration degree, and 13% higher mechanical stability of the hybrid membrane compared to the Nafion XL. Compared to commercial Nafion XL, the rNF-WO-10 hybrid membrane showed an 8.8% and 20% increase in current density of the cell at 0.4 V operating at 80 and 95 °C with 1.89 and 2.29 A/cm², respectively. The maximum power density has increased by 9% (0.76 W/cm²) and 19.9% (0.922 W/cm²) when operating at the same temperatures compared to the commercial Nafion XL membrane. Generally, considering the particular structure of Nafion XL, our Nafion-based membrane with 10 wt% WO₃ (rNF-WO-10) is a suitable PEM with a comparable performance at different operating conditions.

Modifications on Promoting the Proton Conductivity of Polybenzimidazole-Based Polymer Electrolyte Membranes in Fuel Cells

Hydrogen-air proton exchange membrane fuel cells (PEMFCs) and direct methanol fuel cells (DMFCs) are excellent fuel cells with high limits of energy density. However, the low carbon monoxide (CO) tolerance of the Pt electrode catalyst in hydrogen-air PEMFCs and methanol permanent in DMFCs greatly hindered their extensive use. Applying polybenzimidazole (PBI) membranes can avoid these problems. The high thermal stability allows PBI membranes to work at elevated temperatures when the CO tolerance can be significantly improved; the excellent methanol resistance also makes it suitable for DMFCs. However, the poor proton conductivity of pristine PBI makes it hard to be directly applied in fuel cells. In the past decades, researchers have made great efforts to promote the proton conductivity of PBI membranes, and various effective modification methods have been proposed. To provide engineers and researchers with a basis to further promote the properties of fuel cells with PBI membranes, this paper reviews critical researches on the modification of PBI membranes in both hydrogen-air PEMFCs and DMFCs aiming at promoting the proton conductivity. The modification methods have been classified and the obtained properties have been included. A guide for designing modifications on PBI membranes for high-performance fuel cells is provided.

A Review of Recent Developments and Advanced Applications of High-Temperature Polymer Electrolyte Membranes for PEM Fuel Cells

This review summarizes the current status, operating principles, and recent advances in high-temperature polymer electrolyte membranes (HT-PEMs), with a particular focus on the recent developments, technical challenges, and commercial prospects of the HT-PEM fuel cells. A detailed review of the most recent research activities has been covered by this work, with a major focus on the state-of-the-art concepts describing the proton conductivity and degradation mechanisms of HT-PEMs. In addition, the fuel cell performance and the lifetime of HT-PEM fuel cells as a function of operating conditions have been discussed. In addition, the review highlights the important outcomes found in the recent literature about the HT-PEM fuel cell. The main objectives of this review paper are as follows: (1) the latest development of the HT-PEMs, primarily based on polybenzimidazole membranes and (2) the latest development of the fuel cell performance and the lifetime of the HT-PEMs.

Novel proton conducting core-shell PAMPS-PVBS@Fe2TiO5 nanoparticles as a reinforcement for SPEEK based membranes

In this study, new nanocomposite membranes from sulfonated poly (ether ether ketone) (SPEEK) and proton-conducting Fe₂TiO₅ nanoparticles are prepared by the solution casting method. Sulfonated core–shell Fe₂TiO₅ nanoparticles are synthesized by redox polymerization. Therefore, 4-Vinyl benzene sulfonate (VBS) and 2-acrylamide-2-methyl-1-propane sulfonic acid (AMPS) are grafted on the surface of nanoparticles through radical polymerization. The different amounts of hybrid nanoparticles (PAMPS@Fe₂TiO₅ and PVBS@Fe₂TiO₅) are incorporated into the SPEEK matrix. The results show higher proton conductivity for all prepared nanocomposites than that of the SPEEK membrane. Embedding the sulfonated Fe₂TiO₅ nanoparticles into the SPEEK membrane improves proton conductivity by creating the new proton conducting sites. Besides, the nanocomposite membranes showed improved mechanical and dimensional stability in comparison with that of the SPEEK membrane. Also, the membranes including 2 wt% of PAMPS@Fe₂TiO₅ and PVBS@Fe₂TiO₅ nanoparticles indicate the maximum power density of 247 mW cm⁻² and 226 mW cm⁻² at 80 °C, respectively, which is higher than that of for the pristine membrane. Our prepared membranes have the potential for application in polymer electrolyte fuel cells.

The preparation of novel sulfonated poly(aryl ether ketone sulfone)/TiO2 composite membranes with low methanol permeability for direct methanol fuel cells

A sulfonated poly(aryl ether ketone sulfone) (SPAEKS) with locally dense sulfonic acid groups is synthesized and different amounts of TiO2 is doped into SPAEKS matrix to prepare composite membranes (SPAEKS/TiO2-x). SEM shows that TiO2 in the composite membranes has good dispersibility when TiO2 content is not higher than 3%. The composite membranes show good mechanical properties, dimensional stability and oxidative stability. The proton conductivity of composite membranes is near to that of Nafion 117 membrane and methanol permeability of composite membranes is much lower than that of Nafion 117 membrane. Therefore, the proton selectivity of composite membranes is higher than that of Nafion 117 membrane. In particular, proton selectivity of SPAEKS/TiO2-3% (12.8 × 104 S s cm−3) is four times higher than that of Nafion 117 membrane (3.2 × 104 S s cm−3).